This invention is concerned with improved closures for containers for pressurized fluids and is more particularly concerned with improvement of beverage bottle closures to prevent closure-missiling.
A popular type of glass bottle for beer or carbonated beverages has a neck provided externally with about one and one quarter turns of threads. A closure having an internal seal engaging the mouth of the bottle is threaded onto the neck, the closure threads being formed in situ by a device which rolls threads onto the malleable side wall of the closure cup, using the glass threads of the bottle as a die. In many cases the neck of the bottle below the threads is formed with a circumferential pilfer-proof band about which the skirt of the cap is rolled to lock the cap to the bottle. The cap may be provided with horizontal and/or vertical lines of weakness in the region of the pilfer-proof band which break when the cap is twisted to remove it.
This type of container has inherently had a potentially serious problem -- premature release of the cap, termed "closure-missiling." When the user twists the cap to remove it, 90.degree. of twisting is sufficient to leave only about one turn of thread retaining the cap on the bottle. The initial turning of the cap permits pressurized gas to enter between the side wall of the cap and the bottle, tending to bulge the cap side wall outwardly. The closure has to turn many degrees before venting of the trapped gas can occur. Before this gas can be released to the atmosphere, the pressure build-up in the cap may be sufficient to overcome the tenuous remaining thread engagement and fire the cap into the air like a missile. The potential danger to the user and to bystanders is self-evident.
The broad problem of pressure build-up within bottles or jars and attempts to solve that problem by venting pressurized gas are, of course, not new. See, for example, U.S. Pat. No. 1,739,659 to Spahn; U.S. Pat. No. 2,990,079 to Garvey; U.S. Pat. No. 2,161,097 to Schroder-Nielsen; U.S. Pat. No. 2,144,273 to Raymond; U.S. Pat. No. 1,694,851 to Glass; and U.S. Pat. No. 3,433,379 to Moldavsky et al. In general, attempts have been made in the prior art to modify the bottle or jar or the closure to provide safety vents for the release of excessive fluid pressure. However, the prior art is devoid of any teaching or suggestion of a solution to the cap-missiling problem referred to above, where the problem occurs only when the user commences to remove the closure, pressure maintenance being required at all other times.